Apply the hereunder setting, those setting will array the line "Polar Array" we will copy the line over itself and rotate each copy 10° and we will copy it 17 times. You can adhust the values the way you want it.

Now we will draw two circles on for the external boundaries and one to hide the center of our last array.

There is by the way two solution that hawen't been suggested yet. Its to use the blend tool with a circular spine to make the ladders. It has the advantage of working also on other shapes such as ovals or random forms. One could also do this with auser defined pattern brush
– joojaaApr 11 '16 at 7:51

2

And another simpler solution is to make a dashed stroke circle and give it a width.
– hsawiresApr 11 '16 at 7:53

And another one could use a wrap envelope to bend a straight form into the circle (or a half in fact). Which would make certain task easier.
– joojaaApr 11 '16 at 8:11

What about starting off with Polar Grid? Really surprised haven't seen that suggested.
Double click on the tool and type in the number of Radial dividers.
Very quick - ungroup a few times,
divide
or shapebuilder tool (with alt to remove)and thats it.